Web dryer with fully integrated regenerative heat source

ABSTRACT

Integrated web dryer ( 10 ) and regenerative heat exchanger ( 20 ), as well as a method of drying a web of material using the same. The apparatus and method of the present invention provides for the heating ( 22 ) of air and the converting of VOC&#39;s to harmless gases in a fully integrated manner via the inclusion of a regenerative combustion device as an integral element of the drying apparatus.

This application is a 371 of PCT/US99/09943, filed May 5, 1999, whichclaims benefit of provisional application 60/084,603, filed May 7, 1998.

BACKGROUND OF THE INVENTION

The control and/or elimination of undesirable impurities and by-productsfrom various manufacturing operations has gained considerable importancein view of the potential pollution such impurities and by-products maygenerate. One conventional approach for eliminating or at least reducingthese pollutants is by thermal oxidation. Thermal oxidation occurs whencontaminated air containing sufficient oxygen is heated to a temperaturehigh enough and for a sufficient length of time to convert the undesiredcompounds into harmless gases such as carbon dioxide and water vapor.

Control of web drying apparatus, including flotation dryers capable ofcontactless supporting and drying a moving web of material, such aspaper, film or other sheet material, via heated air issuing from aseries of typically opposing air nozzles, requires a heat source for theheated air. Additionally, as a result of the drying process, undesirablevolatile organic compounds (VOCs) may evolve from the moving web ofmaterial, especially where the drying is of a coating of ink or the likeon the web. Such VOCs are -mandated by law to be converted to harmlessgases prior to release to the environment.

Prior art flotation drying apparatus have been combined with variousincinerator or afterburner devices in a separated manner in which hot,oxidized gases are retrieved from the exhaust of the thermal oxidizerand returned to the drying device. These systems are not consideredfully integrated due to the separation of oxidizer and dryer componentsand the requirement of an additional heating appliance in the dryingenclosure. Other prior art systems combined a thermal type oxidizerintegrally within the dryer enclosure, also utilizing volatile off-gasesfrom the web material as fuel. However, this so-called straight thermalcombustion system did not utilize any type of heat recovery device ormedia and required relatively high amounts of supplemental fuel,especially in cases of low volatile off-gas concentrations. Still otherprior art apparatus combined a flotation dryer with the so-calledthermal recuperative type oxidizer in a truly integrated fashion. Onedisadvantage of these systems is the limitation of heat recoveryeffectiveness due to the type of heat exchanger employed, thuspreventing extremely low supplemental fuel consumption capabilities andoften precluding any auto-thermal operation. This limitation ineffectiveness results from the fact that a heat exchanger with higheffectiveness will preheat the incoming air to temperatures high enoughto cause accelerated oxidation of the heat exchanger tubes which resultsin tube failure, leakage, reduction in efficiency and destruction of thevolatiles. In general, the thermal recuperative type device has areduced reliability of system components such as the heat exchanger andburner due to the exposure of metal to high temperature in-service duty.

Yet another fully integrated system utilizes a catalytic combustor toconvert off-gases and has the potential to provide all the heat requiredfor the drying process. This type system can use a high effectivenessheat exchanger because the presence of a catalyst allows oxidation tooccur at low temperatures. Thus, even a high efficiency heat exchangercan not preheat the incoming air to harmful temperatures. However, acatalytic oxidizer is susceptible to catalyst poisoning by certaincomponents of the off-gases, thereby becoming ineffective in convertingthese off-gases to harmless components. Additionally, catalytic systemstypically employ a metal type heat exchanger for primary heat recoverypurposes, which have a limited service life due to high temperaturein-service duty.

For example, U.S. Pat. No. 5,207,008 discloses an air flotation dryerwith a built-in afterburner. Solvent-laden air resulting from the dryingoperation is directed past a burner where the volatile organic compoundsare oxidized. At least a portion of the resulting heated combusted airis then recirculated to the air nozzles for drying the floating web.

U.S. Pat. No. 5,210,961 discloses a web dryer including a burner and arecuperative heat exchanger.

EP-A-0326228 discloses a compact heating appliance for a dryer. Theheating appliance includes a burner and a combustion chamber, thecombustion chamber defining a U-shaped path. The combustion chamber isin communication with a recuperative heat exchanger.

In view of the high cost of the fuel necessary to generate the requiredheat for oxidation, it is advantageous to recover as much of the heat aspossible. To that end, U.S. Pat. No. 3,870,474 discloses a thermalregenerative oxidizer comprising three regenerators, two of which are inoperation at any given time while the third receives a small purge ofpurified air to force out any untreated or contaminated air therefromand discharges it into a combustion chamber where the contaminants areoxidized. Upon completion of a first cycle, the flow of contaminated airis reversed through the regenerator from which the purified air waspreviously discharged, in order to preheat the contaminated air duringpassage through the regenerator prior to its introduction into thecombustion chamber. In this way, heat recovery is achieved.

U.S. Pat. No. 3,895,918 discloses a thermal rotary regeneration systemin which a plurality of spaced, non-parallel heat-exchange beds aredisposed toward the periphery of a central, high-temperature combustionchamber. Each heat-exchange bed is filled with heat-exchanging ceramicelements. Exhaust gases from industrial processes are supplied to aninlet duct, which distributes the gases to selected heat-exchangesections depending upon whether an inlet valve to a given section isopen or closed.

It would be desirable to take advantage of the efficiencies achievedwith regenerative heat exchange in air flotation dryers.

SUMMARY OF THE INVENTION

The problems of the prior art have been overcome by the presentinvention, which provides an integrated web dryer and regenerative heatexchanger, as well as a method of drying a web of material using thesame. The apparatus and method of the present invention provides for theheating of air and the converting of VOCs to harmless gases in a fullyintegrated manner via the inclusion of a regenerative combustion deviceas an integral element of the drying apparatus. In one embodiment, thedryer is an air flotation dryer equipped with air bars thatcontactlessly support the running web with heated air from the oxidizer.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic representation of one embodiment of the apparatusand process of the present invention;

FIG. 2 is a perspective view of a monolith bed in accordance with thepresent invention;

FIG. 3 is a schematic representation of a second embodiment of thepresent invention;

FIG. 4 is a schematic representation of a third embodiment of thepresent invention;

FIG. 5 is a schematic representation of a fourth embodiment of thepresent invention;

FIG. 6 is a schematic representation of a fifth embodiment of thepresent invention;

FIG.7 is a schematic representation of a single bed regenerativeoxidizer integrated with a dryer; and

FIG. 8 is a schematic representation of the single bed regenerativeoxidizer of FIG. 7.

DETAILED DESCRIPTION OF THE INVENTION

Fundamental to the realization of a fully integrated dryer andregenerative thermal oxidation device is the requirement that all of theenergy needed for the drying process be derived from the combustion andconversion of the evolved VOCs with minimal or no added fuel. Inaccordance with the present invention, it is possible to achieve anauto-thermal or self-sustaining process mode. Many of the VOCs areexothermic in chemical reaction and as such may be considered as fuel inan integrated system displacing supplemental fuel, such as natural gas.The resulting apparatus provides high heat recovery effectivenesssufficient to provide an auto-thermal condition, or at least a veryminimal supplemental fuel input, in a controlled and sustainable mannerwith high reliability of components and nearly complete conversion ofundesirable volatile off-gases to harmless components.

Turning now to FIG. 1, there is shown schematically a single zoneflotation dryer 10 with an integrated regenerative thermal oxidizer 20.The flotation dryer 10 includes a web inlet slot 11 and web outlet slot12 spaced from the web inlet slot 11, through which a running web 13 isdriven. In the dryer 10, the running web is floatingly supported by aplurality of air bars 14. Although preferably the air bars 14 arepositioned in staggered opposing relation as shown, those skilled in theart will recognize that other arrangements are possible. To achieve goodflotation and high heat transfer, HI-FLOAT® air bars commerciallyavailable from MEGTEC Systems are preferred, which float the web 13 in asinusoidal path through the dryer 10. Enhanced drying can be achieved byincorporating infrared heating elements in the drying zone. The upperand lower sets of air bars are in communication with respective headers16, 16′, each of which receives a source of heated air via supply fan17, and directs it to the respective air bars 14. A make-up air damper25 is provided in communication with fan 17 to supply make-up air to thesystem where necessary. Those skilled in the art will appreciate thatalthough a flotation dryer is illustrated, dryers where contactlesssupport of the web is not necessary are also encompassed within thescope of the present invention.

The regenerative oxidizer 20 that is integrated with the dryer 10 ispreferably a two-column oxidizer, although one column (FIGS. 7 and 8)with the burner in the inlet plenum or three or more columns or a rotarystyle could be used. With regenerative thermal oxidation technology, theheat transfer zones in each column must be periodically regenerated toallow the heat transfer media (generally a bed of ceramic stoneware orsaddles) in the depleted energy zone to become replenished. This isaccomplished by periodically alternating the heat transfer zone throughwhich the cold and hot fluids pass. Specifically, when the hot fluidpasses through the heat transfer matrix, heat is transferred from thefluid to the matrix, thereby cooling the fluid and heating the matrix.Conversely, when the cold fluid passes through the heated matrix, heatis transferred from the matrix to the fluid, resulting in cooling of thematrix and heating of the fluid. Consequently, the matrix acts as athermal store, alternately accepting heat from the hot fluid, storingthat heat, and then releasing it to the cold fluid.

The alternating of the heat transfer zones to provide matrixregeneration is accomplished via suitable switching valves. In oneembodiment of the present invention, there is one switching valve perheat transfer zone, and preferably the switching valves are pneumaticpoppet type valves whose switching frequency or cycle is a function ofvolumetric flow rate such that a reduced flow allows longer periodsbetween switches. While the switching valves provide the means formatrix regeneration, the act of regeneration in itself results in ashort duration emission of untreated fluid direct to atmosphere, causinga lowering of the volatile organic compound (VOC) destructionefficiency, and in cases involving high boiling point VOC's, potentialopacity issues, unless some method of entrapment of this switching airis employed. Preferably, then, an entrapment chamber 90 is used toincrease the efficiency of the apparatus.

FIG. 1 shows generally at 10 a two-column regenerative thermal oxidizer.The gas to be processed is directed from the dryer enclosure 10 to theoxidizer 20 via exhaust fan 30 and suitable ductwork, through suitableswitching valve or valves 21, and into (or out of) one of the heatexchange media-filled regenerative heat exchange columns 15, 15′. Acombustion zone 18 having associated heating means such as one or moregas-fired burners 22 with associated combustion blower 23 and gas linevalving is in communication with each regenerative heat exchange column15, 15′, and is also in communication with dryer supply fan 17. Ideally,operation of the combustion zone heating means is necessary only duringstart-up, to bring the combustion zone 18 and heat exchange columns 15,15′ up to operating temperature. Once operating temperature is achieved,the heating means is preferably turned off (or placed in “pilot model”)and an auto-thermal condition maintained. Suitable combustion zone 18operating temperatures are generally within a range of 1400-1800° F.Those skilled in the art will appreciate that although the term“combustion zone” has typically been used in the industry to identifyelement 18, most or all of the combustion may take place in the heatexchange beds, and little or no combustion may actually take place inthe combustion zone 18. Accordingly, use of this term throughout thespecification and claims should not be construed as implying thatcombustion must take place in that zone.

Preferably the heat exchange columns 15, 15′ are oriented horizontally(i.e., the flow of gas therethrough proceeds in a horizontal path) inthe apparatus in order to economize space. In order to minimizeundesirable accumulation of process gas and induce even distribution ofprocess gas throughout the heat exchange media, preferably a combinationof randomly packed media that includes voids which allow the passage ofgas through the media particles, and structured media is used. In apreferred embodiment, the voids in the randomly packed media are largerthan the voids existing in the interstices formed amongst the mediaparticles. If the voids are too small, the gas will tend to flow in theinterstices rather than through the voids in the particles. Theseexchange particles are fabricated of a single material and arecharacterized by protrusions or vanes extending from the center of theparticle. Spaces between the protrusions provide an ideal void fractionfor the passage of gases, thereby improving the pressure dropcharacteristics of the aggregate heat exchanger bed. This random packedmedia can also have a catalyst applied to the surface.

Those skilled in the art will recognize that other suitable shapes forthe randomly packed media of the present invention can be used,including saddles, preferably ½″ saddles, etc..

A second portion of the heat exchange media is a monolithic structureused in combination with the aforementioned randomly packed media. Themonolithic structure preferably has about 50 cells/in², and allows forlaminar flow and low pressure drop. It has a series of small channels orpassageways formed therein allowing gas to pass through the structure inpredetermined paths. Suitable monolithic structures are mullite ceramichoneycombs having 40 cells per element (outer diameter 150 mm×150 mm)commercially available from Porzellanfabrik Frauenthal GmbH. In thepreferred embodiment of the present invention, monolithic structureshaving dimensions of about 5.91″×5.91″×12.00″ are preferred. Theseblocks contain a plurality of parallel squared channels (40-50 channelsper square inch), with a single channel cross section of about 3 mm×3 mmsurrounded by an approximately 0.7 mm thick wall. Thus, a free crosssection of approximately 60-70% and a specific surface area ofapproximately 850 to 1000 m²/m³ can be determined. Also preferred aremonolithic blocks having dimensions of 5.91″×5.91″6″. In someapplications, a catalyst is applied to the monolith surface.

The relatively high flow resistant randomly packed portion of the mediais preferably placed where the process gas to be treated enters the heatexchange column, thereby effectively assisting in distribution of thegas across the column cross section. The relatively low flow resistantmonolithic portion of the media is preferably placed on the outlet ofthe randomly packed media, where gas distribution has already occurred.Inside a regenerative bed where oxidation is occurring, the exitingsection of the bed has higher fluid temperatures than the inlet section.Higher temperature means both increased viscosity and increased actualvelocity of the fluid, which then generate an elevated pressure drop.Thus, use of the structured media, which has an inherently lowerpressure drop, in this portion of the column is advantageous.

Those skilled in the art will appreciate that a multi-layer bed of heatexchange media can consist of more than two distinct layers of media.For example, the randomly packed media at the inlet of a column can be acombination of different size saddles, such as a first layer of ½″saddles followed by a second layer of 1″ saddles. The monolithic layerwould then follow towards the outlet of the column. Similarly or inaddition, the monolithic layer could be e.g., a first layer of monolithshaving channel cross-sections of 3 mm×3 mm, followed by a second layerof monoliths having channel cross-sections of 5 mm×5 mm. In a systemwhere only a single heat exchanger column is used, the multi-layer mediabed can be a first layer of randomly packed media, a second layer ofmonolithic media, and a third layer of randomly packed media. Thoseskilled in the art will appreciate that the particular design of themulti-layer bed depends on desired pressure drop, thermal efficiency andtolerable cost.

Most preferred is a 100% monolith structure, as shown in FIG. 2. In thehorizontal arrangement shown, the blocks are stacked to build thedesired cross-sectional flow area and the desired flow length. Toconstruct an integrated dryer with a regenerative oxidizer, including anentrapment chamber, which will fit into existing process lines such as agraphic arts printing press line, a compact heat exchange bed isrequired, which is best obtained with the monolith bed. An alternatemonolith bed design would have a catalyst applied to the monolithsurface. For a 100% monolith structure, the uniformity of the air flowinto the monolith is critical to heat exchanger performance. In FIG. 1,flow spreading or distributing devices 95, such as perforated plates,are employed at the inlet and outlet of each column to evenly distributeair flow through the heat exchanger bed. Such flow distributors becomeoptional where randomly packed media is used, since the randomly packedmedia helps distribute the air flow.

Suitable valving 40 is provided to direct gases to atmosphere or topurging inside the apparatus enclosure (or entrapment chamber 90) foroptimal destruction efficiencies.

Suitable pressure and/or temperature attenuators 92 may be provided asshown in order to dampen the effects of valve switching during cyclingof the regenerative heat exchanger. This valve switching can createpressure pulses and/or temperature spikes which can adversely affectdryer operation. The pressure pulses may enter the dryer through the hotair supply line and upset the slightly negative pressure (relative toatmosphere) of the dryer enclosure. This would allow solvent laden airto spill out of the dryer web slots. Temperature fluctuations whichmight occur during the switching process would make it more difficult tocontrol the dryer air temperature at the desired setpoint. Theattenuator 92 could reduce pressure pulses by introducing a flowresistance in the line feeding the dryer enclosure. The temperaturefluctuations are reduced by introducing a device of high surface areaand high thermal capacity into the flow line to the dryer enclosure.

The oxidizer is integrated with the dryer in the process sense; that is,the apparatus is a compact arrangement whereby the dryer is dependentupon the oxidizer for heat and for VOC clean-up. This can beaccomplished by enclosing the oxidizer and dryer in a single enclosure,or by coupling the oxidizer to the dryer, or placing it in closeproximity to the dryer. The oxidizer also can be heat insulated from thedryer. Preferably there is a common wall between the dryer and the heatexchange bed(s) of the oxidizer.

In one embodiment of the present invention, cooling air can be drawnpast the oxidizer and added to the dryer interior as make-up air. Thisprocedure cools the oxidizer and preheats the make-up air, adding to theefficiency of the system.

FIG. 3 shows a flotation dryer with an integrated regenerative thermaloxidizer as in FIG. 1, except that the dryer is a dual zone dryer with ahot air return. Each zone includes recirculating means 17, 17′ such as afan for supplying the air bars 14 with heated drying impingement air viasuitable ductwork in communication with headers 16, 16′. Most of thesupply of hot air to the first zone is from the regenerative thermaloxidizer, as regulated by the hot supply air valve 41. The second zonereceives its supply of hot air from recirculation.

FIG. 4 shows a flotation dryer with an integrated regenerative thermaloxidizer as in FIG. 1, except that the dryer is a multiple zone dryer(three zones shown) with a hot air return. Each zone includesrecirculating means 17, 17′ such as a fan for supplying the air bars 14with heated drying impingement air via suitable ductwork incommunication with headers 16, 16′. All but the final zone receives mostof the supply of hot air from the regenerative thermal oxidizer, asregulated by the hot supply air valve 41. The final zone receives itssupply of hot air from recirculation.

FIG. 5 shows a flotation dryer with an integrated regenerative thermaloxidizer as in FIG. 1, except that the dryer is a multiple zone dryer(three zones shown) with a hot air return, with the final zone being aconditioning zone. Each zone includes recirculating means 17, 17′ suchas a fan for supplying the air bars 14 with heated drying impingementair via suitable ductwork in communication with headers 16, 16′. Theintegrated conditioning zone is as described in U.S. Pat. No. 5,579,590,the disclosure of which is hereby incorporated by reference. Theconditioning zone contains conditioned air that is substantially free ofcontaminants and is at a temperature low enough to absorb heat from theweb, effectively lowering the solvent evaporation rate and mitigatingcondensation. Pressure control means 45 is provided so that solventvapors will not escape from the dryer enclosure and so that ambientmake-up air can be regulated as required via control means 46.

FIG. 6 shows an embodiment similar to FIG. 5, except that oxidizer purgeto the dryer entrapment chamber (and corresponding valve) is eliminated.An optional catalytic stack cleaner 50 is shown for further destructionof VOCs being exhausted to atmosphere, in order to increase the overallefficiency of the apparatus.

Turning now to FIG. 7, there is shown a single bed oxidizer integratedwith a two-zone air flotation dryer. Exhaust fan 30 draws solvent ladenair from within the dryer enclosure and directs it to the regenerativeoxidizer for treatment. The switching valve(s) 21 directs the air to theinlet side of the heat exchange media bed 15. (The inlet side of themedia bed 15 alternates from one side of the bed to the other accordingto a predetermined switch time.) The heat exchange media bed 15 is asolitary accumulation of material with no occlusion for a combustionchamber. A combustion zone exists within the bed where sufficiently highbulk temperatures occur to convert VOCs to end products of carbondioxide and water vapor. The location and size of the combustion zonemay shift within the media bed 15 according to the particularcombination of solvent/fuel rate, mass air flow rate and switch time.The heat exchange media may be comprised fully of any various types ofrandom packing material or a combination of structured and randomlypacked material. The preferred embodiment is a combination of mediatypes in which the structured media is located at the so-calledcold-faces of the bed and the randomly packed material is positioned inthe center section of the bed. Thus the single bed heat exchangeaccumulation is preferably comprised of, in planar fashion, normal tothe direction of air flow, first a depth of structured media followed bya section of randomly packed media and in turn immediately followed by asecond section of structured media the same depth as the first. Theorientation of the bed may be such that the flow is vertical orhorizontal, but the flow must be normal to the planes of various mediasections.

A suitable heat source such as fuel gas piping or preferably an electricheating element is located in the center, randomly packed media sectionfor purposes of initially heating the exchange bed. It is intended thatthe electric element will be turned off at the time solvent and/or fuelis present in the bed. Preferably a combustible fuel, such as naturalgas, is introduced into the gas to be treated prior to its entry intothe heat exchange bed for purposes of sustaining bed temperatures wheninsufficient amounts of process solvent are available to supportrequired combustion temperatures.

A portion of the combusting gases are drawn from the center of the heatexchange bed for purposes of mixing with and heating the supply airwhich is directed to the web of material 13. The hot gas is drawn fromthe center section of randomly packed material via a hot air collectionplenum 75 which runs longitudinally along the center, randomly packedmedia section. The purpose of the plenum is to draw an even amount ofgas from across the exchange media bed to prevent variations oftemperature within the bed caused by an uneven flow regime.

The final supply air temperature which impinges on the web of material13 is determined by the amount of hot gases mixed with recirculation airprior to the supply fan 17. The amount of hot gases is regulated by thehot air supply valve 4′ that is in communication with the hot aircollection plenum 75 attached to the heat exchange bed.

The regenerative heat source described is capable of supplyingsufficient heat to a dryer consisting of one or more (two shown)distinct control zones as demarcated by individual supply fans. Heatfrom the oxidizer section may be directed to one or more of theindividual zones as needed and under process control. The dryer designmay incorporate one or more cooling zones operating in conjunction withand integrated to heating zone control. The atmosphere within the dryeris actively controlled via a make-up air damper 25.

FIG. 8 depicts the preferred embodiment of a heat exchange bed comprisedof a solitary accumulation of heat exchange material with no enlargedocclusion for a combustion chamber. A described combustion zone existswithin the bed around and about the center of the bed in the directionof flow. The size and location of the combustion zone is determined by asignificant and sufficient rise in the temperature gradient within thebed such that combustion and conversion of volatile gases can occur. Aninlet/outlet air distribution plenum 76 provides even velocity profilesto the cold faces of the heat exchange bed 15. A perforated distributionplate 77 may be provided just prior to the cold faces in the directionof air flow to provide for further evening of the velocity profile priorto entering the heat exchange bed. The heat exchange bed preferablyconsists of structured media 15A, which has excellent efficiency ofpressure loss, and randomly packed media 15B, which allows for ease ofembedding heating coils there within and allows for removal of hot gasto heat the supply air of the drying section. Heating means 60,preferably an electric resistance heating element, is controlled withpower control 61 and heats the bed during start-up. Fuel gas injectionvalving 9 regulates the amount of fuel injected into the effluent tomaintain a minimum combustible atmosphere within the combustion zone soas to support conversion of solvent and fuel to carbon dioxide and watervapor.

In any of the embodiments shown, to improve the VOC destructionefficiency and eliminate opacity issues resulting from matrixregeneration, the untreated fluid can be diverted away from the oxidizerstack and directed into a “holding vessel” or VOC entrapment chamber 90.The function of the entrapment chamber 90 is to contain the slug ofuntreated fluid which occurs during the matrix regeneration process longenough so that the majority of it can be slowly recycled (i.e., at avery low flow rate) back to the inlet of the oxidizer for treatment, orcan be supplied to the combustion blower 23 as combustion air, or slowlybled to atmosphere through the exhaust stack. The untreated fluid in theentrapment chamber 90 must be entirely evacuated within the time frameallotted between matrix regeneration cycles since the process mustrepeat itself for all subsequent matrix regenerations.

In addition to its volume capacity, the design of the entrapment chamber90 internals is critical to its ability to contain and return theuntreated fluid back to the oxidizer inlet for treatment within the timeallotted between heat exchanger matrix regeneration cycles. Anyuntreated volume not properly returned within this cycle will escape toatmosphere via the exhaust stack, thereby reducing the effectiveness ofthe entrapment device, and reducing the overall efficiency of theoxidizer unit.

For some operating conditions, the amount of volatile solvents in thedryer exhaust stream will be less than that required for autothermaloperation. To avoid the use of a combustion burner to providesupplemental energy, supplemental fuel may be introduced into thesystem, such as in the exhaust stream, to provide the needed energy. Apreferred fuel is natural gas or other conventional fuel gases orliquids. The elimination of the burner operation is advantageous becausethe combustion air required for burner operation reduces the oxidizerefficiency and can cause the formation of NO_(x). Introduction of fuelgas can be accomplished by sensing temperature in some location, such asin the heat exchange columns. For example, temperature sensors can belocated in each of the heat exchange beds, about 18 inches below the topof the heat exchange media in each bed. Once normal operation of theapparatus begins, combustible fuel gas is applied to the process gas, bymeans of a T-connection prior to the process gas entering the heatexchange column, based upon the average of the temperatures detected bythe sensors in each heat exchange bed. If the average of the sensedtemperatures falls below a predetermined setpoint, additional fuel gasis added to the contaminated effluent entering the oxidizer. Similarly,if the average of the sensed temperatures rises above a predeterminedsetpoint, the addition of fuel gas is stopped.

Alternatively, combustion zone temperature may be indirectly controlledby means of measuring and controlling the energy content of the exhaustair entering the oxidizer. A suitable Lower Explosive Limit (LEL) sensorsuch as is available from Control Instruments Corporation, can be usedto measure the total solvent plus fuel content of the exhaust air at asuitable point following the pint of supplemental fuel injection. Thismeasurement is then used to modulate by suitable control means theinjection rate of fuel to maintain a constant, predetermined level oftotal fuel content, typically in the range of 5 to 35% of LEL,preferably in the range of 10 to 20% LEL. If the LEL measured by thesensor is below the desired setpoint, the amount of supplemental fuelinjected is increased such as by opening the control valve 9. If the LELmeasured is above the setpoint, the supplemental fuel injection rate isreduced such as by closing the flow valve 9. IN the case that thesolvent content from the drying process is higher than the desired LELsetpoint even with no fuel injection, the exhaust rate from the dryingprocess may be increased to reduce the LEL such as by adjusting flowthrough the exhaust fan 30. This adjustment of exhaust flow is wellknown to those skilled in the art, and is preferably accomplished with avariable speed drive on fan 30, or by a flow control damper.

If the concentration of combustible components in the gas to be treatedbecomes too high, excessive temperatures will occur in the apparatusthat may be damaging. To avoid such excessive temperatures in the hightemperature incineration or combustion zone, temperature can be sensedsuch as with a thermocouple appropriately positioned in the combustionzone and/or in one or more of the heat exchange columns, and when apredetermined high temperature is reached, the gases that normally wouldbe passed through the cooling heat exchange column can be insteadbypassed around that column. When placed in the heat exchange columns,the particular location of the temperature sensors is not absolutelycritical; they can be located six inches, twelve inches, eighteeninches, twenty-four inches below the top of the media, for example.Preferably the sensors are placed from about 12 to 18 inches below thetop of the media. Each sensor is electrically coupled to a controlmeans. A hot bypass duct/damper receives a signal from the control meansthat modulates the damper to maintain a temperature as measured by thesensor to a predetermined set point. Those skilled in the art willappreciate that the actual set point used depends in part on the actualdepth of the temperature sensor in the stoneware, as well as on thecombustion chamber set point. A suitable set point is in the range offrom about 1600° F. to about 1650° F. The bypassed gases can beexhausted to atmosphere, combined with other gases that have alreadybeen cooled as a result of their normal passage through the cooling heatexchange column or used for some other purpose.

What is claimed is:
 1. A dryer for a web of material and having anintegrated regenerative heat source, comprising: a web inlet and a weboutlet spaced from said web inlet; a plurality of nozzles for dryingsaid web; a regenerative heat source comprising at least one heatexchange column, said at least one column having a gas inlet and a gasoutlet, said at least one column being in communication with acombustion zone, and containing heat exchange material; valve means foralternatingly directing gas from said dryer into said inlet of said atleast one heat exchange column; and means in communication with saidcombustion zone for directing a portion of the gas therein to one ormore of said plurality of nozzles.
 2. The dryer of claim 1, whereinthere are at least two heat exchange columns.
 3. The dryer of claim 1,wherein at least some of said plurality of nozzles are flotation nozzlesfor floatingly supporting said web in said housing enclosure.
 4. Thedryer of claim 1, 2 or 3, wherein said heat exchange material is acombination of randomly packed media and structured media.
 5. The dryerof claim 1, 2 or 3, wherein said heat exchange material is a monolith.6. The dryer of claim 2 or 3, further comprising an entrapment chamberhaving an inlet in communication with said valve means.
 7. The dryer ofclaim 1, 2 or 3, further comprising means for introducing a combustiblefuel into said at least one heat exchange column.
 8. The dryer of claim1, 2 or 3, wherein said heat exchange material comprises a catalyst. 9.The dryer of claim 1, 2 or 3, further comprising attenuating means incommunication with said combustion zone.
 10. The dryer of claim 9,wherein said attenuating means attenuates pressure.
 11. The dryer ofclaim 9, wherein said attenuating means attenuates temperature.
 12. Thedryer of claim 1, further comprising temperature sensing means in saidregenerative heat source, and bypass means responsive thereto forextracting a portion of gases from said regenerative heat source whensaid temperature sensing means senses a predetermined temperature. 13.The dryer of claim 1, further comprising a sensor for sensing theconcentration of volatile organic solvent of said gas directed into saidinlet.
 14. The dryer of claim 7, further comprising a sensor for sensingthe concentration of volatile organic solvent of said gas directed intosaid inlet, and wherein the amount of said combustible fuel introducedis responsive to the sensed concentration.
 15. A method of drying arunning web of material, comprising: transporting said web into a dryerhaving a dryer atmosphere; impinging heated gas onto said web with aplurality of nozzles; drawing a portion of said dryer atmosphere into anintegrated regenerative heat source comprising at least one heatexchange column in communication with a combustion zone and containingheat exchange material in order to heat said portion of said dryeratmosphere; combusting in said regenerative heat source volatilecontaminants contained in said dryer atmosphere; and directing a portionof the combusted gas from said regenerative heat source to one or moreof said plurality of nozzles.
 16. The method of claim 15, furthercomprising sensing the concentration of volatile contaminants in saiddryer atmosphere.
 17. The method of claim 15 or 16, further comprisingintroducing a combustible fuel into said at least one heat exchangecolumn.
 18. The method of claim 17, wherein the amount of combustiblefuel gas introduced is responsive to the sensed concentration ofvolatile contaminants.